Figure 2. Ocular hypertension (OHT) promotes retinal tau upregulation and epitope-dependent changes in phosphorylation. A, Intraocular pressure (IOP) measurements for individual rats during a 3 week period following injection of hypertonic saline solution into an episcleral vein (Intact, N = 10; OHT, N = 14). B, Western blot analysis showed a substantial increase in all tau isoforms in retinas with OHT compared with Intact controls. Two examples of retinas with OHT are shown, using different samples and exposure times, to better demonstrate the independent increase of the 50 and 55 kDa bands. C, Densitometry demonstrated a 3.2-fold, 3.4-fold, and 4.9-fold increase in the 50, 55, and 100 kDa bands, respectively, in glaucomatous retinas compared with Intact controls (OHT, N = 10; Intact, N = 6; Student's t test, *p < 0.05, ***p < 0.001). D, Real-time qPCR analysis demonstrated no significant change in retinal tau gene expression (OHT, N = 6; Intact, N = 6). E–G, Western blot analysis of phospho-specific epitopes revealed alterations in tau phosphorylation at PHF1 and PS199, while no change was detected at AT8. H–J, Densitometric analysis demonstrated a significant increase in phosphorylation on S396 and S404 (PHF1), accompanied by reduced phosphorylation on S199 (PS199) relative to total tau, while no change was detected on AT8 (OHT, N = 9–10/group; Intact, N = 6; Student's t test, *p < 0.05, **p < 0.01). Vertical lines represent nonconsecutive samples from the same gel.